(1) Field of the Invention
The present invention relates to control and adjustment means of the type used in electrical instruments and more particularly to a sealed adjusting device having a normally freely turnable or rotatable setting knob that can be actuated temporarily by manual pressure for engagement with an adjustable element so as to change the setting thereof, e.g. for calibrating an electronic or electrical measuring apparatus or for zero-adjustment thereof.
Monitoring and measurement of environmental parameters that have an ecological significance is a problem of growing importance, i.e. to determine the concentration of undesirable components or pollutants in the air or in water; electrical or electronic instruments having a very high sensitivity are required for these purposes. Frequently, such instruments are used under operating conditions that involve contact with water, moisture and other environmental hazards for sensitive instruments, e.g. portable instruments for gas-analytical or limnological measurements.
Frequently, such instruments require a calibration setting or zero-adjustment prior to commencing the actual measuring operation and such adjustment or setting must not be changed unintentionally during operation, i.e. it must be protected against displacement by hazard or mistake.
(2) Description of the Prior Art
Prior art adjustment devices that would be suitable for preventing an accidental change of the setting or adjustment of an instrument are known, such as the device disclosed in German patent application DE-OS No. 1,260,003, but are not generally suitable for use in an unprotected environment; complicated and, hence, costly structural changes would be required to adapt such devices for sealed operation.
Accordingly, it is the main object of this invention to provide for an adjusting device of a simple structure that precludes accidental changes of the setting or adjustment of an instrument while at the same time effectively preventing penetration of water or contaminants into an instrument housing provided with such an adjusting device.